1. Field of the Invention
The invention relates to a method for the production of curved thread-reinforced tubular structures and a device for such production.
2. Background Description
Curved thread-reinforced tubular structures may be used in automobile applications such as, for example, pneumatic springs of motor vehicles. A generic production method and device for curved thread-reinforced tubular structures are known, for example, from DE 25 45 058 C3. In this case, mandrels are guided concentrically by the axis of rotation of a deflection element, so that a constant thread angle, distributed over the circumference, is ensured.
To improve the pneumatic spring properties of the tubular structures, it is known from DE 196 14 476 A1 and EP 0 285 726 B1 to vary the thread angle over the length of the pneumatic springs. Due to the varied thread angle in the axial direction of the pneumatic spring bellows, the latter has a differing outside diameter according to the thread angle, so that the rolling behavior and the air pressures can be adapted to the respective requirements involved in the installation and operation of the pneumatic spring bellows in a pneumatic spring.
The winding of reinforcing threads on to mandrels guided in a feed direction, with a rubber layer extruded on them, is known, for example, from DE 198 46 852 C2. In this case, the reinforcing threads are guided in a deflection element on the inner circumference of the deflection element with a very small gap with respect to the mandrel. The reinforcing threads are guided to the outer circumference of the mandrel or of the rubber layer located on it by means of guides distributed equidistantly on the inner circumference of the deflection element. In this situation, the deflection element rotates at a speed corresponding to a required thread angle with respect to the feed direction.
When, for example, the pneumatic springs are installed in vehicles, the installation situation is sometimes so unfavorable that curved pneumatic springs have to be used. Curved tubular structures are conventionally produced by straight thread-reinforced tubular portions being prestressed into a curved shape and then vulcanized. Such a method is described, for example, in DE 25 45 058 C3. One disadvantage, however, is that the run of the reinforcing threads during production is not adapted to the curved shape. During prestressing, a displacement of the reinforcing threads which is detrimental to the quality of the final product then sometimes occurs. Moreover, only a complete curvature of the tubular portion is possible, but not the production of selected curved regions.